Plastic Injection Molding: Improving Manufacturing Quality
Plastic Injection Molding
Details
Details:
Model
Material
Brand
Origin
Application
Booling-Injection-1
P20, 718, S136, 2738 etc
Booling
China
Automotive parts, industrial parts, medical parts, household
The production method of plastic injection molding technology is crucial, and manufacturers need to control temperature, pressure, and time during the manufacturing process, considering how to improve manufacturing quality.
Advantages of Plastic Injection Molding：
- High Precision and Repeatability
- Low Cost per Part
- Fast Production Rate
- Wide Material Choice
- Little Waste
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Plastic injection molding is a plastic processing technology, which is mainly based on the plasticity and squeezability of plastics. The main process is to melt loose plastic particles and powders in the barrel, creating a flowing state, and inject them into a closed mold through a nozzle. At this time, the manufacturer’s control of injection molding pressure and temperature is crucial. After curing and cooling, it is demolded into a molded part.
Best Solution for Color Change of Plastic Injection Molded Parts
Manufacturers often require parts of different colors for plastic injection molding, and the color of the parts frequently changes with the temperature during plasticization. Even if there is a difference of 10 ℃, color deviation may occur.
When the Color of the Injection Molded Part Does Not Deviate Significantly from the Sample
When encountering such situations, manufacturers can solve the problem by adjusting the temperature. In general, adjusting the processing temperature range of the raw materials up and down by 5-15 degrees Celsius can significantly change the color and reduce the color deviation. In most cases, lowering the temperature will make white plastic parts whiter and ordinary plastic parts darker in color; Raising the temperature will make the color of the plastic parts lighter, and the white plastic parts will turn yellow. But for special parts, such as fluorescent injection molded parts, the color changes can make manufacturers more elusive.
When the Color of the Injection Molded Part Deviates too much from the Sample
If the color deviation between the actual produced parts and the samples is too large to be solved by adjusting the temperature, the company needs to notify the color matching personnel to perform color matching, which can reduce many subsequent color matching times. Color matching needs to be carried out at the temperature suitable for the production of the product, but remember to do it at the injection molding temperature required for the production of the plastic product. Due to the significant impact of temperature on the color of the injection molded parts, manufacturers must monitor and adjust temperature changes promptly during production. Once the color has been debugged and put into use, the temperature fluctuation range during plastic injection molding should be kept within plus or minus 5 ℃, and jumping within a large temperature range is no longer allowed. For some light-colored plastics that are greatly affected by temperature, manufacturers even need to control the drying temperature and time well and pay attention not to be too high or too long, otherwise, it will lead to unstable color production of the parts, especially for products with fluorescent and purple colors. Therefore, the issue of moisture in plastics requires a long period of baking to solve, so manufacturers should bake before color matching.
The Influence of Color and Ingredient Selection on the Strength of Plastic Parts
The influence of different color ingredients on the strength of injection molded parts is significant, and the effect brought by using titanium dioxide and color varieties is completely different.
- Strength Defects Caused by Color Matching with Different Colors
-Reason
After melting, the color seeds need to be thoroughly mixed with the raw materials in the heating cylinder of the injection molding machine. Color matching is different from color powder. Color powder can be mixed evenly with raw materials in advance in the roller feeding machine, so when using color matching, injection molded parts are prone to color mixing or uneven color matching problems.
-Solution
If manufacturers cannot solve the problems of color mixing and brittleness, and use color matching in the color matching stage, they may consider replacing it with color powder matching, which will improve the defects of the parts to a certain extent.
-Special Phenomena
Manufacturers should also note that when producing black or injection molded parts that require the addition of black color seeds, the amount of black material cannot be directly seen from the color. Therefore, sometimes the batching workers do not strictly follow the requirements of the formula to mix the proportion of black seeds and add black seeds as they please during the batching process. Therefore, there are often situations where more black seeds are added, and in some cases, manufacturers are afraid that the purity of black is not enough and intentionally add excessive black seeds, which can lead to the brittleness of black injection molded parts even when used less in secondary recycling. In addition, white injection molded parts are usually colored with titanium dioxide. The more titanium dioxide there is, the whiter the injection-molded parts become, and at the same time, the injection-molded parts also become brittle. The precautions for adding titanium dioxide are similar to those for adding black seeds.
- The Influence of Titanium Dioxide Content in White Injection Molded Parts on Strength
Titanium dioxide is a type of metal powder, so it cannot blend and fully mix with plastics. It is equivalent to an impurity in plastic injection molding, which destroys the structure of the plastic and the connection between it and the adhesive. Therefore, the strength of plastic will continuously decrease with the increase in the amount of titanium dioxide added. After reaching a certain critical value, PVC injection molded parts will become adhesive-like and can be easily pulled and twisted. In addition, in areas with weld marks, the strength of injection molded parts will decrease even more severely. Therefore, under the condition of meeting the color requirements for the whiteness of injection molded parts, the content of titanium dioxide should be minimized as much as possible.
Improvement of Dimensional Accuracy of Injection Molded Parts
When manufacturers produce high-precision plastic parts through plastic injection molding, the allowable tolerance range is very small, so at this time, manufacturers need to find ways to improve the accuracy of the plastic parts.
-Shrinkage Rate
In the process of injection molding production, the shrinkage rate of injection molded parts is usually the main factor affecting the dimensional accuracy of injection molded parts. The larger the shrinkage rate, the worse the accuracy of injection molded parts, such as PP and POM materials. The products formed by injection molding of these two materials have a large shrinkage rate, and the accuracy of their injection molded parts is usually poor, with low yield and consistency. The shrinkage rate of other materials is usually not very small, so under general conventional injection molding conditions, the dimensional accuracy of injection molded parts is not very high.
-Adjust the Machine
Adjustment is an effective means to improve the dimensional accuracy of injection molded parts. Manufacturers only need to significantly increase the injection or holding time and pressure to reduce the shrinkage rate, and the shrinkage of injection molded parts can also be reduced to a certain extent, naturally improving the dimensional accuracy. However, due to quality limitations, the injection pressure of general injection molding machines cannot be adjusted too high, otherwise, a large amount of overflow will occur, resulting in a significant amount of labor costs in the future. Therefore, manufacturers mainly rely on increasing the injection or holding time on commonly used injection molding machines to reduce shrinkage and improve the dimensional accuracy of injection molded parts.
-Precision of Molds
Mold is the beginning and key to plastic injection molding. To ensure the dimensional accuracy of injection molded parts, manufacturers first need to ensure the accuracy of the mold, and then choose a stable and reliable (with little parameter fluctuation) injection molding machine with sufficient pressure. This is very important for the production of plastic injection molding. At present, in the plastic injection molding industry, most of the newly developed high-precision injection molding machines are high-pressure injection molding machines with stable performance and extremely high parameter accuracy. The shrinkage rate of its injection molded parts is very small, even almost zero. That is to say, every time this injection molding machine is used to produce injection molded parts, the size is almost as long as the cavity size, without obvious shrinkage marks, and the fluctuation range is even within 0.01mm. The accuracy can be described as extremely high.
The technology of plastic injection molding has high production efficiency and features low cost and high precision. Widely used in the automotive industry, furniture, medical equipment, electronics industry, etc.
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